those clickbank offer which ask u key in email

so the lead the vendor get will they follow up your afflaite links back end?

this is what I always curious and doubt about it or they just promote themselves keep the leads promote their own stuffs

Yes. Some vendors are really shady.

I know for example that a vendor named John Crestani overwrites your affiliate ID with his own after the 3rd email that gets sent out.

This is a way of shaving. Some even go as far as to use this tactic by retargeting on Facebook.